The Senate Democratic Leader is the floor leader of the Democratic Party in the United States Senate.

The position of Democratic Leader dates to 1920, when the Senate's Democratic caucus first elected a member to this position. (By comparison, the Republicans first elected a floor leader in 1925.) Depending upon which of the two parties holds the majority of votes in the Senate at a time, the Senate Democratic Leader is either the Majority Leader or the Minority Leader. If the two parties are equal in strength in the Senate, which last occurred in 2001, the party of the President is considered the majority party, as his Vice President will naturally be of his party and the Vice President has a tie-breaking vote in the Senate in all matters, including organizational ones.

In recent years it has become more common for the leader of the majority to party to be referred to as the "Majority Leader" and the leader of the minority party to be referred to as the "Leader" of his party in order to reduce the (correct) implication that "Minority" connotes of lesser power. The outgoing Senate Democratic Leader is Tom Daschle of South Dakota, who lost his seat in South Dakota to Republican Rep. John Thune in the 2004 elections. The first floor leader to lose reelection in more than half a century, Daschle's loss set the stage for a major restructuring of the Senate Democratic leadership.

Democratic whip Harry Reid of Nevada, New York Sen. Charles Schumer, Connecticut Sen. Christopher Dodd, and Delaware Sen. Joe Biden were considered to be the major contenders to succeed Daschle in the 109th Congress in January 2005, with the position eventually going to Reid.

Many state senates are organized in the same fashion as the United States Senate.